0 Assigned ID: 1189 ----- Attempting Submission 1 (Fri Apr 07 23:54:48 GMT 2017) ----- HST Phase I Proposal 1189 (HST2017.apt) successfully submitted. Receipt: # 1189-1 ----- Attempting Submission 2 (Sat Apr 08 00:00:37 GMT 2017) ----- In recent years, HST surveys such as CANDELS, HUDF, BoRG/HIPPIES, ERS, and the Frontier Fields, have made possible the first robust measurements of the rest-frame UV luminosity function of z =6-10 galaxies, spanning much of the redshift range over which reionization likely occurred. These measurements provide an estimate of the galactic ionizing photon output, addressing the critical question of whether these galaxies could have reionized the Universe. In addition, follow-up spectroscopy has measured the fraction of these galaxies that show Lyman-alpha emission. Interestingly, a dramatic decrease in this fraction above z~6 has been observed, and this evolution has (controversially) been interpreted as evidence that much of reionization happened over z=6-8 (as intergalactic neutral gas leads to large damping wings that scatter the Lyman-alpha line). The clumpiness of the IGM and how it self shields to ionizing photons impacts whether the observed population of galaxies can reionize the Universe, as well as the interpretation of the evolving Lyman-alpha emitter fraction. We propose to run fully coupled radiative-hydrodynamics simulations that are the first to resolve the evaporation of small structures by passing ionization fronts and, hence, to accurately assess the level of clumpiness and self-shielding from the IGM. Our study will nail down the "clumping factor" used to assess whether the observed population of galaxies can drive reionization, and it will address whether neutral self-shielding clumps in recently reionized regions can scatter galaxies' Lyman-alpha lines. Cosmology Galaxies and the IGM 0 Regular false false true SUPPORTED